Electrode joint

ABSTRACT

A furnace electrode assembly of the type including a pair of electrode sections having tapered threaded sockets and a nipple threaded into each of the sockets to hold the sections in faceto-face contact is characterized by a pair of counterbores at the bottom of the sockets and a portion at the center of the nipple which is devoid of threads.

United States Patent Q 6/1950 Johnsoner Lewis Feb. 29, 1972 [54]ELECTRODE JOINT 3,016,343 1/1962 Krenzke 287/127 E X [72] Inventor: JohnG- Lewis Ann Arbor Mich. 3,540,764 11/1970 Paus ..13/18 X [73] Assignee:Air Reduction Company, Incorporated, Primary Gilheany New york, yAssistant Examiner-R. N. Envall, Jr. [22] Pl d A 28 1970 Attorney-EdmundW. Bopp and H. Hume Mathews le 1 8- 9 1 21 Appl. No.: 67,818 Y [57]ABSTRACT A furnace electrode assembly of the type including a pair ofelectrode sections having tapered threaded sockets and a nip- [52]U.S.Cl ..l3/18, 287/127 E ple threaded into each of the sockets to holdthe Sections in [51] '3" "Hosb 7/06 face-to-face contact ischaracterized by a pair of counterbores [58] Field of Search ..13/18;287/127 E at the bottom f the Sockets and a portion at the center of thenipple which is devoid of threads. [56] References Cited 7 Claims, 2Drawing Figures UNITED STATES PATENTS Pate nted Feb. 29, 1972 2Sheets-Sheet 1 FIG.

I N Vli'N'l ()R JOHN G, LEWIS Pa ented Fb.29, 1972 3,646,240.

I 2 She ets-Sheei; 2 I

FIG, 2

. INVENTOR.

' JOHN. GyLEWIS This invention relates generally to electric furnaceelectrodes, and more specifically relates to an electrode assembly ofthe type including abutting carbon or graphite electrode sections, whichare securely held in face-to-face relationship by a nipple threaded intoa socket in each section.

Electrode assemblies of the type indicated in the foregoing paragraph,generally comprising carbon, graphite, or a similar carbonaceousmaterial, are widely utilized in the electric furnaces of the steelmaking and metal-smelting industries. In the environments to which suchassemblies are exposed in these industries, the electrodes andconnecting nipple are subjected to great thermal stresses, and to impactloading which occurs, for example, when the electrode assembly is struckby falling scrap or the like. As the electrode assembly is already underconsiderable mechanical stress, due both to the requirement that issupport its own weight and to effects resulting from the torque used totighten the joint, the added thermal and impact stresses often resultsin failure of the joint, with cracking or splitting occurring either inthe electrode sections, in the nipple, or in both. Such defects will ata minimum result in power being wastefully dissipated at thehigh-resistance breaks rather than in the metallurgical processeswherein the energy is intended to be dissipated; in other instancescomplete breakage of the joint may ensue, with resulting collapse of theelectrodes into the melt.

In accordance with the foregoing, it is an object of the presentinvention to provide an electrode joint assembly exhibiting increasedability to withstand thermal and impact loading.

It is a further object of the invention to provide an electrode assemblywith increased capabilities for elastic deflection.

It is another object of the invention to provide an electrode assembly,the construction of which prevents the buildup of destructive stressconcentrations, such as in thread roots at the base of the electrodesocket.

It is a yet further object of the invention to provide a nippleconstruction for use with electric furnace electrodes, which increasesthe ability of an electrode assembly utilized therewith to withstandelastic deflection, such as that imposed by impact loading.

It is an additional object of the invention to provide electrodesections for use with a connecting nipple in an electric furnaceenvironment, which sections are possessed of increased elasticdeflection properties when in assembly with said nipple, and whichmoreover include transition for fro transferring the load from theelectrode sections to the joint threads and back, without developing thedestructive stress concentrations evidenced in conventional structures.

SUMMARY OF THE INVENTION In accordance with the present invention, theforegoing objects, and others as will become apparent in the course ofthe following description, are achieved by an electrode joint assemblywhich includes a nipple having a center portion which is unthreaded andof reduced cross section, and a pair of abutting electrode sectionswhich are provided with deep counterbores at the internal terminationsthereof, the said electrode sections being preferably provided as wellwith a BRIEF DESCRIPTION OF DRAWINGS The invention is diagrammaticallyillustrated, by way of example, in the appended drawings, in which:

FIG. 1 is a vertical cross section through an electrode assembly inaccordance with the invention, and illustrates in a generalized fashionthe principal features thereof; and,

FIG. 2 is a diagrammatic vertical section of the assembly, and setsforth various parameters significant to the practice of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, a vertical section isshown of an assembly 3 in accordance with the invention. As seentherein, a pair of female electrode sections 4 and 5, typically formedof graphite, carbon, or the like are in face-to-face relationship, withthe abutting faces being held in firm contact by the nipple 9, which isthreaded into each of the sections 4 and 5 and is formed of materialcorresponding (essentially identical) to that in the electrode sections.The use of a nipple in the manner set forth to yield an assembly of thisgeneral type is conventional, the assembly typically being formed byfirst inserting the nipple into one threaded socket 6 of a femalesection and then threading the other section about the nipple until atight joint is achieved.

The nipple 9 shown in FIG. 1, unlike conventional nipple constructionsof the prior art, is not shaped so as to essentially conform to theinternal cavity defined by sockets 6, but rather includes a centerportion 11 which is not only devoid of threads, but which is moreover atthe center thereof reduced in cross section as compared to the endportion of the nipple. As a result, nipple 9 is actually in threadedcontact with sections 4 and 5 only at the ends thereof beyond theportion 11.

The electrode sections 4, 5 in addition to having the usual threadedsockets 6 therein, include at the terminations of sockets 6, contiguous,voluminous counterbores 7 and 8,

which smoothly merge with the threaded sockets 6. The sections 4 and 5also may include shallow relief grooves 2 in their abutting faces.

The specific characteristics of the assembly 3 construction shown inbroad outline in FIG. 1, are best seen in the diagrammatic depiction ofFIG. 2. With respect firstly, to the nipple 9, it is seen therein thatthe nipple 9 is of length M, and differs from conventional constructionsin having a center unthreaded portion 11 of length L. This portion 11 isof a reduced cross section, the minimum diameter D being not greaterthan the minor diameter of the first adjacent thread and preferablybeing less than the minor diameter C of the small end threads ofsections 4, 5. (Typically C-D='k inch for nipples for 20 or 24 inchelectrodes.) This portion 11 not only renders the nipple better able toabsorb impact loads elastically, but as portion 11 will stretch fartherunder a given preload, it will tend too to keep the joint tight withinreasonable limits of mismatch of the coefficient of thermal expansion ofthe electrode and nipple. The length L in a typical 20 or 24 inchdiameter (.I graphite electrode joint may be in the range of 2 to 9inches; while the upper end of this range permits a higher degree offlexure in the joint under dynamic loa;ing, account must also be takenof stresses induced by shear deflection of the remaining threads ofnipple and socket under dynamic loading. The shear deflection referredto occurs much as though thin coaxial cylinders of graphite slide overeach other like the sections of a telescope. In consideration of thisfactor, it is preferably for L to be at the lower end of the range cited(preferably about 10 to 15 percent of the diameter of the electrodejoint), the reduced tensile deflection resulting from a shorter value ofL being more than offset by the increased number of threads which cansimultaneously carry load because of the flexibility in shear justmentioned.

The reduced portion 11 of nipple 9 is typically formed to be equivalentto a standard nipple from which the center threads have been machined toyield a straight section of length N and diameter D, an arc OP (which isa surface of revolution) being formed to smoothly connect the thusreduced section with the remaining threads at the end of the nipple.This smooth arc OP serves to transfer the load from electrode proper tothe joint threads without destructively concentrating stress.

The counterbores 7 and 8 of FIG. 1 and 2 are produced by removingmaterial below thethreaded socket 6 of electrode sections 4 and 5 to adiameter A, not less than minor diameter C of the small end nipplethreads; preferably A is somewhat greater than B, the major diameter ofthe large end threads in a typical case A is about 1 inch larger than Bfor or 24 inch electrodes. The largest practical fillet radius, e.g.,radius of 6 inches, is used to join minor diameter of threads and thebore diameter and to terminate the bore in a rounded bottom.

The counterbores 7 and 8 provide a portion of electrode which is lessstifi than the electrode proper and thereby serve as transition zonesbetween the electrode and the joint. As was mentioned in connection withare OP, the surface of revolution represented by arc EFG serves totransfer the load from electrode proper to joint threads and back againwithout destructive concentration of stress. It should be noted,however, that arcs EF, EG, and OP, all may be made parabolic.

The shallow relief grooves 2, described in connection with FIG. 1, areseen in FIG. 2 to extend out from the large end of sockets 6 to adiameter specified as I. I will typically exceed dimension B by from 2to 4 inches in the case of the typical 20 or 24 inch electrode. i.e.,(l-B) will representatively be of the order of 9 to 20 percent the valueof dimension J. Grooves 2 will representatively be less than 0.100 inchin depth.

Grooves 2 aid the socket threads to deflect more nearly as a unit, andalso tend to force the compressive reactions on the electrode sectionfaces to occur farther away from the CD. of the socket threads. Thissalutary effect is enhanced and compounded by the construction referredto, wherein dimension D is made less than C, and A is made greater thanB.

While the present invention has been particularly described in terms ofspecific embodiments thereof, it will be apparent that numerousvariations may be made without departing from the invention.Accordingly, the present invention is to be broadly construed, andlimited only by the scope and spirit of the claims appended hereto.

Iclaim:

1. In a furnace electrode assembly of the type including a pair ofelectrode sections having tapered threaded sockets therein and a nipplethreaded into each of said sockets and holding said sections in firmface-to-face contact, the improvement comprising:

a. a pair of counterbores at the bottom of said sockets, of

diameter at least as great as the small end diameter of said socket;

b. said nipple including a portion at the center thereof which is devoidof threads and includes a cross section of diameter less than the minordiameter of the first adjacent thread thereto; and

c. shallow recessed relief grooves being formed in the abutting faces ofsaid electrode sections, said grooves being concentric with said nippleand sockets and extending outward from said socket.

2. Apparatus in accordance with claim 1 wherein the diameter of saidcounterbore is grater than the large end diameter of said sockets.

3. Apparatus in accordance with claim 2 wherein said counterbores aresmoothly jointed to said small ends of said sockets by surfaces ofrevolution.

4. Apparatus in accordance with claim 1 wherein said nipple portiondevoid of threads includes a center length of uniform diameter less thanthe minor diameter of the small end of said sockets, said center lengthbeing smoothly joined to threads present at the alternate ends of saidnipple by surfaces of revolu,ion.

5. In a furnace electrode assembly of the type including a pair ofelectrode sec,ions having tapered threaded sockets therein and a nipplethreaded into each of said sockets and holding said sections in firmface-to-face contact, the im-t provement wherein:

said nipple includes a portion at the center thereof which is devoid ofthreads and includes a center length of uniform diameter less than theminor diameter of the small end of said sockets, said center lengthbeing smoothly oined to threads present at the alternate ends of sardnrpp e by surfaces of revolution.

6. In a furnace electrode assembly of the type including a pair ofelectrode sections having tapered threaded sockets therein and a nipplethreaded into each of said sockets and holding said sections in firmface-to-face contact, the improvement comprising: a pair of counterboresat the bottom of said sockets, the diameter of said counterbore beinggreater than the large end diameter of said sockets.

7. Apparatus in accordance with claim 6, wherein said counterbores aresmoothly joined to said small ends of said sockets by s$rfaces ofrevolu,ion.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIDN Patent No.,646,240 Dated February 29, 1972 Inventor(s) John G; Lewis It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as show below:

Column l, line &9, after "transition" insert the word zones a line &9,delete "fro Column 2-, line 56, "loa ing should read loading line 62,"preferably" should read preferable Column 3, line 17, "Ed" should readFG Column line 12, "grater" should read greater line 15, "jointed"should read joined line 22, "revolu,ion" should read revolution line 24,"sec,ions" should read sections line &3, ".s$.rfaces" should readsurfaces line #3, revolu,ion" should read revolution Signed and sealedthis 11th day of July 1972.

( SEAL) Attest:

EDWAR D I LFLETC HER, Jll R0 BERT GOTTSCHALK .Attestinp; OfficerCommissioner of Patents F ORM PO-1050 (10-69) USCOMM-DC 60376-P69 u.s.GOVERNMENT PRINTING OFFICE I969 0-366-334 UNlTED STATES PATENT OFFICE ICERTIFECATE OF QORREfi'llQN Patent No. 3,646,240 Dated February 29, 1972Inventor(s) John G. Lewis It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 1, line 2-9, after "transition" insert the word zones line 49,delete "fro'.

Column 2, line 56, "loa;ing" should read loading line 62, "preferably"should read preferable Column 3, line 17, "Ed" should read FG Columnline 12, "grater" should read greater line 15, "jointed" should readjoined line 22, "revolu,ion" should read revolution line 24, "sec,ions"should read sections line 43, "s$rfaces" should read surfaces line 43,revo1u,ion" should read revolution Signed and sealed this 11th day ofJul; 1972.

(SEAL) Attest:

EDWARD I LFLETCHER T ROBERT GOTTSCHALK Attestinp; Officer Commissionerof Patents FORM PO-1050 (10-69) USCOMM'DC 50376-1 69 U.S GOVERNMENTPRINTING OFFICE: I969 O-366-335

1. In a furnace electrode assembly of the type including a pair ofelectrode sections having tapered threaded sockets therein and a nipplethreaded into each of said sockets and holding said sections in firmface-to-face contact, the improvement comprising: a. a pair ofcounterbores at the bottom of said sockets, of diameter at least asgreat as the small end diameter of said socket; b. said nipple includinga portion at the center thereof which is devoid of threads and includesa cross section of diameter less than the minor diameter of the firstadjacent thread thereto; and c. shAllow recessed relief grooves beingformed in the abutting faces of said electrode sections, said groovesbeing concentric with said nipple and sockets and extending outward fromsaid socket.
 2. Apparatus in accordance with claim 1 wherein thediameter of said counterbore is grater than the large end diameter ofsaid sockets.
 3. Apparatus in accordance with claim 2 wherein saidcounterbores are smoothly jointed to said small ends of said sockets bysurfaces of revolution.
 4. Apparatus in accordance with claim 1 whereinsaid nipple portion devoid of threads includes a center length ofuniform diameter less than the minor diameter of the small end of saidsockets, said center length being smoothly joined to threads present atthe alternate ends of said nipple by surfaces of revolution.
 5. In afurnace electrode assembly of the type including a pair of electrodesections having tapered threaded sockets therein and a nipple threadedinto each of said sockets and holding said sections in firm face-to-facecontact, the improvement wherein: said nipple includes a portion at thecenter thereof which is devoid of threads and includes a center lengthof uniform diameter less than the minor diameter of the small end ofsaid sockets, said center length being smoothly joined to threadspresent at the alternate ends of said nipple by surfaces of revolution.6. In a furnace electrode assembly of the type including a pair ofelectrode sections having tapered threaded sockets therein and a nipplethreaded into each of said sockets and holding said sections in firmface-to-face contact, the improvement comprising: a pair of counterboresat the bottom of said sockets, the diameter of said counterbore beinggreater than the large end diameter of said sockets.
 7. Apparatus inaccordance with claim 6, wherein said counterbores are smoothly joinedto said small ends of said sockets by surfaces of revolution.